1. Field of the Invention
The present invention relates to a method for preparing a high purity light gas consisting of a member selected from the group consisting of hydrogen or helium. More particularly, the present invention relates to a method for preparing a light gas consisting of hydrogen or helium and having a high purity of 99.99 molar % or more when a content of water is omitted from the calculation of the purity, by a multiple step gas-separating procedure in which a feed gas to be purified is selectively permeated successively through a plurality of gas-separating polymeric membrane modules.
The term "light gas" used herein refers to a gas consisting essentially of hydrogen or helium.
Also, the term "gas-separating membrane module" used herein refers to a module comprising at least one polymeric membrane which selectively allows a light gas to permeate therethrough to concentrate the light gas and to separate impurities other than water therefrom.
2. Description of the Related Arts
In a known method used industrially a hydrogen or helium gas is concentrated or refined from a mixture gas containing hydrogen or helium by a low temperature processing method or an absorption method, and recently, it has become known that the concentration or refining of the hydrogen or helium gas can be conducted by using a gas-separating polymeric membrane.
But this polymeric membrane gas-separating method has the following advantages and disadvantages.